1. Field of the Invention
This invention relates to a method for a balancing centering of workpieces which are to be machined only at certain portions, particularly crankshafts, wherein the workpiece is displaced transversely to its axis of rotation so as to reduce the unbalance before the workpiece is machined, and the workpiece is subsequently cut to length and is formed in its end faces with centering bores which define a center line and an axis of rotation, of a balanced workpiece. The invention relates also to a machine for carrying out that method.
2. Description of the Prior Art
Owing to the steady progress which has been achieved in forging and foundry technology, even workpieces used as rotating parts of machines, such as crankshafts and camshafts, need no longer be finished by a machining of all portions of the rough workpiece in an as-cast or as-forged state. It is often sufficient to machine the workpiece only at its bearing and sliding surfaces and possibly at surfaces at which the workpiece is to be clamped and engaged for alignment and at other critical surface portions so that the manufacture of the workpiece will be more economical. But it is still necessary to balance the workpiece in a final operation, in which considerable difficulties will arise if the masses are not properly distributed. For a mass balancing, material must be removed from the workpiece by drilling or boring and a satisfactory balancing may not be accomplished in extreme cases, in which an adequate mass cannot be removed from the workpiece by drilling or boring. In order to simplify that final balancing, it has been suggested to perform a preliminary centering and balancing of the workpieces before they are machined. In that case the workpiece is displaced transversely to its ideal geometrical axis of rotation in dependence on the unbalance which has been detected and when the workp8iece is in a corrected position the centering bores are formed so as to define the new position of the center line and the axis of rotation of the workpiece so that the initially present unbalances are compensated. In the previous practice, the entire mass of the workpiece and the mass distribution of the entire workpiece was taken into consideration and formed the basis for determining the balancing centering, and a dynamic balancing of the workpiece has been effected although this is a complicated operation and does not produce satisfactory results as the subsequent machining of parts of the workpiece will change the masses and the mass distribution so that the final balancing of the finished workpiece is hardly simplified.